Electrical power networks have historically been hierarchical in nature, with power generation facilities feeding electrical power into the network at one end, and a range of customers drawing power from the network at another end (logically speaking). Such an arrangement is convenient to the power distribution companies because when maintenance work needs to be carried out on the network, circuit breakers at strategic points can be opened thereby isolating the relevant parts of the network and allowing work to proceed safely.
The concept of “feed-in tariffs” changes this fundamentally. According to this concept, end-user customers are given the option to install local power generation facilities, usually a renewable energy source such as solar panels, wind turbines or the like. These are connected to the electrical distribution network and, if they generate more: power than the customer needs, feed the excess power back into the network. The customer is then paid for the electrical power they supply into the network.
This means that the distribution company has lost a degree of control over its network. During repair work, it can isolate sections of network from its own power generation facilities but cannot be certain that there are no customer feed-in points that are supplying power. Accordingly, the section of network may still be live, despite being isolated. During normal operation, the company will need to monitor the network in order to determine what power is actually being transmitted in order to ensure that demand is met appropriately. Distribution companies therefore need to be able to check on the local voltage, current and phase angle at distributed locations on the network. At least one such company has issued a requirement for a means of doing so; so far the proposals for doing so involve severing the cable just short of a connection, and splicing on a short section of cable that includes the necessary passive sensors and which is terminated with a standard connector via which it can be re-connected.
Such modifications need to be suited to underground (insulated) power cables. Generally, this problem does not apply in the case of suspended power lines as customer feed-in points will be on the distribution grid rather than the transmission grid. The transmission grid usually employs uninsulated extra-high-voltage cables (typically 100 kV and upwards) that are suspended from pylons in free air, which therefore acts as an insulator and a source of cooling. This is used for long-range transmission of power from medium to large power plants; only very large industrial customers take power directly from the transmission grid, and such customers do not qualify for domestic feed-in tariffs. Distribution grids accept power from nodes in the transmission grid at lower voltages of (typically) 50 kV or below, and connect to smaller industrial customers, substations for domestic customers, and feed-in points such as wind farms, solar farms, small power plants, and domestic feed-in points. These connections are often via insulated cables, which may be buried, enclosed in conduits, or suspended at lower levels.